Fibroblast cells with mitochondria shown in greenFLICKR, D. BURNETTE, J. LIPPINCOTT-SCHWARTZ/NICHDSince the 1970s, when researchers turned up similarities between DNA in eukaryotes’ mitochondria and bacterial genomes, scientists have suspected that the organelles descended from symbionts that took up residence within larger cells. A diverse class of bacteria called Alphaproteobacteria soon emerged as a likely candidate for the evolutionary origins of mitochondria. But a new analysis, published today (April 25) in Nature, suggests that mitochondria are at best distant cousins to known alphaproteobacteria lineages, and not descendents as previously thought.
“We are still left hungry for the ancestor of mitochondria,” says Puri Lopez-Garcia, a biologist at the University of Paris-South who was not involved in the study.
While it’s generally agreed that Alphaproteobacteria includes the closest bacterial relatives of mitochondria, that relationship doesn’t reveal much about how mitochondrial ancestors made a living or how they made the jump to acting as organelles. That’s because “Alphaproteobacteria is a particularly diverse group of organisms in terms of kinds of metabolism,” Lopez-Garcia explains. “You find more or less everything in there.” Some studies have found genetic similarities between mitochondria and an order of alphaproteobacterial symbionts known as Rickettsiales, but other, free-living candidates have also emerged.
I do find myself with as many questions at the end of reading ...
